A defibrillator is a medical device designed to deliver a controlled electrical shock to the heart. This intervention aims to reset the heart’s electrical activity when it experiences life-threatening rhythm disturbances, such as ventricular fibrillation or pulseless ventricular tachycardia. The energy delivered is measured in joules, which helps restore a normal heart rhythm. Defibrillators stop chaotic electrical signals that prevent the heart from pumping blood effectively.
Common Defibrillator Joule Settings
Defibrillator joule settings vary depending on the device type and patient’s age. For adult defibrillation, manual defibrillators use different joule ranges based on waveform technology. Older monophasic defibrillators deliver a single electrical pulse in one direction, requiring 360 joules for adults.
In contrast, modern biphasic defibrillators deliver current in two directions, allowing for lower energy levels to achieve similar outcomes. The recommended initial dose for biphasic defibrillation in adults is between 120 and 200 joules. Some protocols may recommend increasing the energy for subsequent shocks if the initial one is unsuccessful, potentially up to 300 or 360 joules.
Automated External Defibrillators (AEDs) are designed for use by laypersons and deliver fixed, pre-set energy levels. For adults, AEDs administer a biphasic shock in the range of 150 to 200 joules. These devices automatically analyze the heart’s rhythm and advise if a shock is needed, without requiring the user to manually select the energy level.
Pediatric defibrillation requires lower, weight-based energy levels to account for children’s smaller body size and cardiac mass. The initial energy dose for pediatric patients is 2 joules per kilogram (J/kg) of body weight. If the first shock is unsuccessful, subsequent shocks may be delivered at 4 J/kg, with some guidelines allowing for escalation up to 10 J/kg or the adult maximum dose.
What Determines Defibrillator Energy Levels?
The selection of appropriate joule settings is influenced by several factors related to the patient and the device. Patient factors include body size and weight, especially for pediatric patients who require weight-based dosing to prevent myocardial damage from excessive energy. Underlying medical conditions can also play a role in determining effectiveness.
The type of cardiac rhythm being treated is another determinant. Different arrhythmias respond to varying energy levels; for instance, ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT) are shockable rhythms that require immediate defibrillation. Other arrhythmias, like atrial fibrillation or ventricular tachycardia with a pulse, might be treated with synchronized cardioversion, which uses lower, synchronized energy levels.
The device type, specifically whether it uses a monophasic or biphasic waveform, directly impacts the required energy. Biphasic devices are more efficient and can achieve successful defibrillation with lower joule settings compared to monophasic devices. Modern defibrillators, including AEDs, predominantly utilize biphasic waveforms.
The number of shocks delivered can also influence energy levels; if an initial shock is unsuccessful, successive shocks may use escalating energy levels, although some biphasic protocols maintain a fixed energy for repeated shocks. Using the correct joule setting maximizes the chance of restoring a normal rhythm while minimizing potential heart muscle damage. Transthoracic impedance, the resistance to current flow through the chest, can affect the current delivered, and some biphasic devices adjust energy based on this.